1. Field
The present disclosure relates to an accelerator pedal apparatus applied to vehicles such as automobiles, and in particular, relates to an accelerator pedal apparatus which includes a reaction force adding control mechanism which attracts a driver's attention to accelerator pedal operation by varying operational reaction force.
2. Description of the Related Art
Recently, accelerator pedal apparatuses having a reaction force adding control mechanism to vary operational reaction force against accelerator pedal operation have been developed and adopted for vehicles such as automobiles. The variation of operational reaction force due to the reaction force adding control mechanism is to attract the driver's attention. Since large variation of the operational reaction force may surprise a driver to cause incorrect operation of the accelerator pedal, it is necessary to avoid worsening the operational feeling of the accelerator pedal. Particularly, in an accelerator pedal apparatus targeting to achieve eco-driving (i.e., to improve fuel consumption), it is important to attract the driver's attention while maintaining excellent operational feeling of an accelerator pedal.
For example, Japanese Laid-open Patent Publication No. 2010-52721 discloses a technology to prevent flipping of an accelerator pedal against a driver's intentions by increasing operational reaction force of the accelerator pedal when accelerator opening reaches an accelerator opening threshold value for worsening of fuel Consumption and cancelling the increased amount of the operational reaction force when the accelerator opening is decreased to be equal to or smaller than an increased amount cancellation threshold value which is smaller than the accelerator opening threshold value by a predetermined amount.
In Japanese Laid-open Patent Publication No. 2010-52721 of the related art, a countermeasure to suppress accelerator pedal flipping by varying accelerator opening threshold values for increasing and decreasing the operational reaction force is implemented against a phenomenon that the accelerator pedal is returned as being bounced owing to momentum of pedaling force increase of the accelerator pedal when operational reaction force is added to the accelerator pedal. In this case, it is required for the accelerator opening to keep difference to some extent between the accelerator opening threshold value for operational reaction force adding and the accelerator opening threshold value for operational reaction force cancelling. Accordingly, there has been a problem that an accelerator opening capable of improving fuel consumption (i.e., an eco-driving point) is difficult to be recognized by a driver.
Based on studies as focusing on accelerator pedal behaviors at the time of adding operational reaction force to the accelerator pedal, the inventors have revealed that reaction force feelings obtained at the time of adding operational reaction force to the accelerator pedal are different between those in depressing and returning of the accelerator pedal even if the same operational reaction force with the same stroke amount is added.
FIG. 7 illustrates a basic pedaling force characteristic (hereinafter, called a basic pedaling force characteristic F0) of an accelerator pedal of which operational reaction force is not increased by a reaction force adding control mechanism. An appropriate hysteresis characteristic (i.e., a hysteresis amount ΔF) is provided between a depression direction (arrow A) in which the accelerator opening is enlarged with depressing of the accelerator pedal and a return direction (arrow B) in which the accelerator opening is lessened with returning of the accelerator pedal. Here, the operational reaction force F in the depression direction is set to be larger than the operational reaction force F in the return direction even at the same accelerator opening. Since the appropriate hysteresis characteristic is provided as described above, the accelerator opening can be easily maintained at constant owing to the hysteresis amount ΔF even when accelerator depressing force is varied to some extent.
In FIGS. 8A to 8C, a dotted line indicates a basic pedaling force characteristic line of the basic pedaling force characteristic F0 and a solid line indicates an operational reaction force characteristic line (hereinafter, called increased operational reaction force Fi) in a state that adjustment force ΔFa (i.e., operational reaction force) is added to the basic pedaling force characteristic F0 by the reaction force adding control mechanism. When the adjustment force ΔFa (i.e., the operational reaction force) is added by the reaction force adding control mechanism, it is shifted to the operational reaction force characteristic line in the return direction (arrow B′) of the operational reaction force characteristic line of the increased operational reaction force Fi in every case that accelerator operation before the adjustment force ΔFa (i.e., the operational reaction force) is added is in the depression direction, in the return direction, or in a stopped state. When pedaling force being ΔFb or larger is applied as the driver continues to further depress the accelerator pedal against the operational reaction force, it is shifted to the operational reaction force characteristic line in the depressing direction (arrow A′) of the operational reaction force characteristic line of the increased operational reaction force Fi. Accordingly, as long as pedaling force being ΔFb or larger is not applied to the accelerator pedal by the driver after the operational reaction force is added, the operational reaction force F is increased by the amount of ΔFa-ΔF as illustrated in FIG. 8A when the adjustment force ΔFa is added to the basic pedaling force characteristic F0 by the reaction force adding control mechanism while the accelerator pedal operation is in the depression direction (arrow A). When the adjustment force ΔFa is added to the basic pedaling force characteristic F0 by the reaction force adding control mechanism while the accelerator pedal operation is in the return direction (arrow B), the operational reaction force F is increased by the amount of ΔFa as illustrated in FIG. 8B. When the adjustment force ΔFa is added to the basic pedaling force characteristic F0 by the reaction force adding control mechanism while the accelerator pedal operation is in a stopped state, the operational reaction force F is increased by the amount in a range between ΔFa-ΔF and ΔFa as illustrated in FIG. 8C in accordance with the depression force of the accelerator pedal. In this manner, the increased amount of the operational reaction force F is varied in the range between ΔFa-ΔF and ΔFa depending on the operational direction of the accelerator pedal as being influenced by the hysteresis characteristic.
As described above, the same reaction force feeling cannot be provided to the driver even if the same operational reaction force at the same stroke amount is added to the accelerator pedal. Accordingly, when trying to recognize the eco-driving point, the driver feels a sense of strangeness as causing worsened operability. Since the above contributes to accelerator pedal flipping and disturbs fuel consumption improvement, an accelerator pedal especially targeting eco-driving (i.e., fuel consumption improvement) cannot achieve the primary target.